A known injector device of this kind comprises a body endowed with a pressure chamber which is open at one of its ends, communicating with a steam inlet and from the bottom of which a liquid supplying nipple extends with its orifice communicating with a liquid inlet. The mouth of the pressure chamber has fitted therein a nozzle having an outlet orifice for the liquid-steam mixture and communicating with a hole which surrounds the nipple, thus forming an annular gap about the lateral surface of the nozzle. The steam stream issuing from this gap thus causes a Venturi effect which sweeps the liquid present in the nipple orifice.
In some applications, for example when this injector device is used in a machine for the treatment of textiles, the need arises for varying the flow rate of the delivered liquid, in order to meet the requirements of the treatment to be performed, by means of a corresponding variation of the pressure of the steam supplied to the pressure chamber.
It has been experienced, in practice, that the flow rate of the liquid supplied by this injector device is weakly sensitive to the pressure variations of the carrier steam. In other words, to attain the liquid flow rates that are necessary in some applications, it is necessary to generate high steam pressures which are incompatible with the structural features of the usual machines and steam supplying plants.
On the other hand, experience has demonstrated that this known injector device provides a correct admixture of the steam with the liquid only within very narrow limits of the steam pressure, which when the correct admixture is not obtained leads to an uneven liquid distribution within the projected jet, the more so in the case of nozzles having a slit shaped outlet orifice to give a jet in configuration of a flat fan.